1. Field of the Invention
The present invention relates to a sustaining manipulator arm. More particularly, the present invention relates to a sustaining manipulator arm with a multi-degree-of-freedom motion and being capable of reaching static equilibrium.
2. Description of the Related Art
A static balancing mechanism is capable of keeping the mechanism at static equilibrium at any stop position during a motion process. This kind of mechanism can be widely applied in supporting or pick-and-place mechanisms, such as: a table lamp, an operation lamp, a monitor support bracket, a manipulator arm, and so on. For example, this kind of mechanism can also be applied in U.S. Pat. No. 6,328,458 (Bell et al., Dec.11, 2001), U.S. Pat. No. 4,080,530 (Krogsrud, Mar. 21, 1978), U.S. Pat. No. 4,796,162 (Krogsrud, Jan. 3, 1989) and U.S. Pat. No. 5,618,090 (Montague et al., Apr. 8, 1997). The static balancing mechanism can be accomplished by counterbalancing, spring balancing or many other equivalent methods. The method of adding a spring utilizes a spring potential energy change to balance a gravitational potential energy change of the mechanism, thereby achieving a conservative energy system which keeps the total potential energy unchanged. Comparing to the method of counterbalancing, the method of adding a spring causes a relatively small burden to the overall weight of the system, and the spring is characterized in low cost and easy production.
Most conventional spring static balancing mechanisms cannot reach complete gravitational equilibrium at an arbitrary position due to the limitation of the structure arrangement or spring installation position of the mechanism. Therefore, a conservative energy system cannot be accomplished, thus resulting in imperfect balance. Further, a conventional spring static balancing mechanism is mostly composed of a planar mechanism or multiple vertical planar mechanisms, which are assembled by multiple planar parallelogram linkages. However, due to the limitation of the planar structure, even though vertical rotary shafts have been added to increase one degree of freedom of the mechanism in a horizontal motion under the condition of keeping the operational plane of the planar parallel four-bar linkages perpendicular, three spatial rotational degrees of freedom motion still cannot be accomplished.
Further, in known prior arts, the axial direction of a revolution element (such as a revolute pair) of a known parallelogram linkage must be in a horizontal direction, and the motion track of a coupler of the parallelogram linkage is a circular route. With regard to a known parallelogram linkage structure, no matter how two or multiple parallelogram linkages are connected, it can only perform planar motion. Therefore, it can only reach limited positions.
For example, U.S. Pat. No. 3,973,748 (Nagasaka, Aug. 10, 1976) discloses a structure composed of a basic planar parallelogram connecting bar and a diagonal spring. A cam is added to an extended point of the spring, to improve the balance caused by a friction condition change.
U.S. Pat. No. 4,160,536 (Krogsrud, Jul. 10, 1979) discloses a structure composed of two connected parallelogram arms. A nylon shoe is connected to a slide, such that a spring can be hidden from view, and different counterbalancing forces can be reached by utilizing the slide to adjust the position.
Therefore, there is a need to provide a sustaining manipulator arm, which can reach static equilibrium when the manipulator arm stays at an arbitrary position, and can perform a multi-degree-of-freedom motion, to mitigate and/or obviate the aforementioned problems.